This should not be confused with parody advertisements, where a fictional product is being advertised for the purpose of poking fun at the particular advertisement, nor should it be confused with the use of a coined brand name for the purpose of comparing the product without actually naming an actual competitor. ("Wikipedia tastes better and is less filling than the Encyclopedia Galactica.")
the other candidate is displayed, for the purpose of disparaging the other candidate. The most famous of these type ads, which only ran once on TV, consisted of a child picking daisies in a field, while a voice which sounded like Barry Goldwater performed a countdown to zero before the launch of a nuclear weapon which explodes in a mushroom cloud. The ad was produced by Lyndon B. Johnson's campaign in an attempt to prevent Goldwater from either winning the nomination of his party or being selected.
Another example took place throughout starting in circa 1986, between the bitter rivalry between Nintendo and Sega. "Genesis does what Nintendon't" immediately became a catchphrase following the release of the Sega Genesis (known as Mega Drive in PAL countries).